Automation System
A disadvantage of Numerical Control (NC) is:

the machine tool can easily overheat
the tape and tape reader are not reliable
None of these
the computer is not reliable
one operator is needed for each machine.

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Automation System
Time proportioning control:

cannot use a TM990 micro¬computer
a and b above.
is less efficient than normal PID control
can be used on a PM550 programmable process controller
None of these

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